1. Field of the Invention
The present invention relates to a pretensioner for a seat belt retractor, and more particularly, to a pretensioner for a seat belt retractor a capable of forcedly winding a webbing on a torsion bar upon abrupt deceleration of a vehicle due to collision, and so on, to prevent the webbing from being loosened.
2. Description of the Conventional Art
A conventional seat belt retractor employs a pretensioner for forcedly winding a webbing on a torsion bar upon abrupt deceleration of a vehicle due to collision, and so on, to prevent the webbing from being loosened.
Several examples of the conventional seat belt retractor will be described below.
Conventional Art 1
Typical structure of the pretensioner is disclosed in Japanese Patent Laid-open Publication No. 2000-302012, entitled “Webbing Winding Device,” which will be described in brief.
The webbing winding device includes a winding shaft to which a base end of a long strip-shaped webbing belt for restricting a passenger's body is fixed and to which force is applied in a direction winding the webbing belt, a pretensioner for rotating the winding shaft in the winding direction under a predetermined condition, a bearing means having an inner periphery into which the winding shaft is inserted on a shaft having an inner diameter larger than an outer diameter of the winding shaft, and a projection projecting from one of the inner periphery of the bearing means and the outer periphery of the winding shaft toward the other, and contacting the other at a very small area in comparison with the area of the other opposite to the one.
Conventional Art 2
In addition, Japanese Patent Laid-open Publication No. 2000-302013 discloses “Pretensioner,” which will be described in brief.
The pretensioner is integrally formed with a webbing winding device for winding a webbing for restricting a passenger on a winding shaft in a layered manner to rapidly rotate the winding shaft in a webbing winding direction to a predetermined extent using a rack/pinion type drive mechanism upon rapid deceleration of a vehicle. The drive mechanism includes a piston movably disposed in a cylinder in an axial direction and having a rack bar to be moved upon rapid deceleration of the vehicle, and a pinion disposed to be meshed with a rack gear of the piston and directly connected to a shaft end of the winding shaft through the medium of a clutch connected to the winding shaft upon rapid deceleration of the vehicle.
Conventional Art 3
Further, Japanese Patent Laid-open Publication No. 2003-335217 discloses a safety belt retractor, which will be described in brief.
The safety belt retractor includes a housing having a pair of side plates, a winding shaft rotatably supported between the side plates of the housing and rotatably biased in a webbing winding direction, and a pretensioner mechanism attached to one side plate of the housing to rotate the winding shaft in the winding direction and wind the webbing upon rapid deceleration of a vehicle.
The pretensioner mechanism includes a gas generator for generating a gas, a cylinder having one end on which the gas generator is mounted and the other end installed at an outer surface of the one side plate of the housing at its one side, and a pinion gear interlocked with the winding shaft to be rotatably supported by the winding shaft.
In addition, a piston is installed at a base end to be movably accommodated in the cylinder to be driven by a gas pressure, and a rack is formed at a front end of the piston to be meshed with the pinion gear. The rack is meshed with the pinion gear depending on the compression driving of the piston to rotate the winding shaft in the winding direction.
Further, the retractor includes a cover body for forming a movement guide path of the rack disposed on an extension line of the other end of the cylinder and projecting from the other end of the cylinder, a first adhesion part installed at the one side plate of the housing to cover an opening at the other side of the cylinder in a manner adhered to the piston, and a second adhesion part installed at the cover body to cover the opening of the other side of the cylinder in a manner adhered to the piston.
Conventional Art 4
In addition, Japanese Patent Laid-open Publication No. 2004-1777 discloses a pretensioner, which will be described in brief.
The pretensioner is integrally formed with a webbing winding device for winding a webbing for restricting a passenger on a winding shaft in a layered manner to rapidly rotate the winding shaft in a webbing winding direction to a predetermined extent using a rack/pinion type drive mechanism upon rapid deceleration of a vehicle.
The drive mechanism includes a piston movably disposed in a cylinder in an axial direction and having a rack bar to be moved upon rapid deceleration of the vehicle, and a pinion disposed to be meshed with a rack gear of the piston and directly connected to a shaft end of the winding shaft through the medium of a clutch connected to the winding shaft upon rapid deceleration of the vehicle.
The pinion includes a gear part having a pinion gear meshed with the rack gear, and a clutch part integrally formed with the gear part in a concentric manner and having the clutch formed at an inner periphery thereof.
Conventional Art 5
First, Japanese Patent Registration No. 3519302 discloses a typical pretensioner structure, which will be described below in brief with reference to FIGS. 1A to 1C.
As shown, a retractor 38 of Conventional Art 5 includes a housing 12 fixed to a vehicle, and a torsion bar 14 rotatably installed at the housing 12. A webbing 16 is wound on the torsion bar 14.
In addition, the retractor 38 includes a piston-gear type pretensioner 10 for a seat belt retractor. A gear member 18 is connected to one end of the torsion bar 14. Therefore, rotation of the gear member 18 causes rotation of the torsion bar 14 to wind the webbing 16.
Further, a cylinder 20 is fixed to the housing 12. The cylinder 20 has a hollow cylindrical shape, a tip 22 of which is opened adjacent to the gear member 18.
Meanwhile, a cylindrical recess 26 is formed at a bottom surface 24 of the cylinder 20. The recess 26 has a diameter smaller than an inner diameter of the cylinder 20 such that a position of an O-ring 34 is determined depending on constitution of the bottom surface 24 and the recess 26 of the cylinder 20. In addition, a gas supply port (not shown) is formed at the recess 26 to allow supply of a gas into the cylinder 20 when the vehicle is abruptly decelerated.
Further, a substantially circular pressure receiving plate 28 is installed in the cylinder 20 to move in the cylinder 20. As a result, when a gas is supplied into the cylinder 20, the pressure receiving plate 28 moves along an arrow (direction C) of FIG. 1C.
In addition, a piston 30 is integrally formed with a surface of the pressure receiving plate 28 facing the gear member 18. A rack formed at one side of the piston 30 corresponds to the gear member 18. When the piston 30 moves with the pressure receiving plate 28 in the arrow direction C of FIG. 1C, the rack of the piston 30 is meshed with the gear member 18 to rotate the gear member 18 in a direction that the webbing 16 is wound (an arrow A of FIG. 1C).
Meanwhile, a cylindrical seal holding part 32 is integrally formed with the pressure receiving plate 28 facing the bottom surface 24 of the cylinder 20, and the O-ring 34 is disposed on an outer periphery of the seal holding part 32. The O-ring 34 has an elasticity to seal between the pressure receiving plate 28 and an inner wall 36 of the cylinder 20.
In addition, the O-ring interposed between the pressure receiving plate 28 and the bottom surface 24 of the cylinder 20 prevents the pressure receiving plate 28 from being in direct contact with the bottom surface 24 of the cylinder 20. In this state, the position of the pressure receiving plate 28 is an initial position (an initial assembly position) of the pressure receiving plate 28. Here, the seal holding part 32 is disposed in the recess 26 of the bottom surface 24 of the cylinder 20, with the O-ring 24 being in contact with the bottom surface 24 of the cylinder 20. Further, the recess 26 has a depth such that the seal holding part 32 is not in contact with a bottom surface 27 of the recess 26 even when the O-ring is elastically deformed.
Meanwhile, since the piston-gear type pretensioner for a seat belt retractor of Conventional Art 5 includes a force limiter (not shown), when the force limiter is operated, the gear member 18 is rotated in a counter-winding direction of the webbing 16 to release the webbing 16, thereby preventing a passenger from receiving a load more than a predetermined amount.
Eventually, in the case of the pretensioner of Conventional Art 5, the recess 26 having a diameter smaller than an inner diameter of the cylinder 20 is formed at the bottom surface 24 of the cylinder 24, and a step is formed between the inner wall 36 of the cylinder 20 and an inner wall of the recess 26. In addition, the O-ring 34 is disposed on the step.
Since the step narrows a space between the bottom surface of the recess 26 and a lower end of the seal holding part 32, a gas pressure provided through the gas supply port may be insufficiently transmitted to the pressure receiving plate.
In addition, according to Conventional Art 5, a portion of the cylinder adjacent to the gas support port may be weak to be readily broken on gas discharge.
Conventional Art 6
Japanese Patent Registration No. 3819189 discloses a constitution of a pretensioner, which will be described with reference to FIG. 2.
As shown, since a piston head 20 of a piston 22 of Conventional Art 6 maintains a state extended in an initial assembly position to a bottom position in which a straight section of the piston accommodating part 30 of the cylinder 24 is terminated, there is an insufficient space to be pressed by the discharged gas.
In addition, since the cylinder has a small thickness at its corners in which a gas pressure is largely applied and abruptly changes its direction, the corners of the cylinders may be damaged on gas discharge.
Conventional Art 7
Japanese Patent Registration No. 3218987 discloses a constitution of a pretensioner for a seat belt retractor, which will be described with reference to FIG. 3.
As shown, since a piston head 7 of a piston 25 of Conventional Art 7 also maintains a state extended from an initial assembly position to a bottom position in which a straight section of the piston accommodating part of the cylinder 24 is terminated, there is an insufficient space to be pressed by the discharged gas.
In addition, since the cylinder has a small thickness at its corners in which a gas pressure is largely applied and abruptly changes its direction, the corners of the cylinders may be damaged on gas discharge.
Conventional Art 8
Japanese Patent Laid-open Publication No. 1995-251710 discloses a constitution of a pretensioner for a seat belt, which will be described with reference to FIG. 4.
As shown, the pretensioner for a seat belt of Conventional Art 8 includes an ignition propulsion wadding material operated by a fuse 48 and adapted to a drive device for the seat belt pretensioner, and the drive device includes a piston 18 for performing translation movement of a piston-cylinder unit.
However, in the seat belt pretensioner of Conventional Art 8, since an end of the piston 18 is disposed on a step of an inner wall of a cylinder 16 to maintain an initial assembly state, an area on which a gas pressure is applied is reduced to decrease operation efficiency of the gas pressure against a lower end of the piston 18.
Conventional Art 9
Great Britain Patent GB1162323 discloses a constitution of a pretensioner for a seat belt, which will be described with reference to FIG. 5.
As shown, since a piston head 26 of a piston 25 of Conventional Art 9 also maintains a state extended from an initial assembly position to a substantially bottom position of the piston accommodating part of the cylinder 24, there is an insufficient space to be pressed by the discharged gas.
As described above, since the piston head of the piston is disposed at a lower end of a straight movable guide of the cylinder on initial assembly to form an insufficient space under the piston head, or a step formed at a lower end of the cylinder also narrows the space, it is difficult to sufficiently apply a predetermined gas pressure to a pressure receiving plate.